This invention pertains to pre-manufactured housing units, more particularly to a pre-manufactured housing unit designed with a foundation structure, integral frame and supports to withstand appreciable sag or flex in the foundation.
Harsh environments, such as the frozen tundras of Alaska, demand that suitable housing units be extremely weatherable. The conditions created by such harsh climates creates problems not currently being addressed in the pre-fabricated housing market. Existing housing units are designed to be supported at many different load bearing points along their foundation, thereby creating a transportation problem when moving the unit to its ultimate location. Such homes can not be stacked on top of one another since all load bearing points could not be equally supported, especially the ones in the interior foundation. Thus, relocation from manufacturer to end user requires sophisticated and expensive moving equipment.
Typical housing units are built with a beam in the middle of the foundation structure running lengthwise of the structure. Transverse beams are then located between the middle longitudinal beam, and extending outward to the sides of the unit. The outer longitudinal beams as well as the middle beam require a number of support posts and pads. A typical problem encountered with conventional post and pad configurations is differential settling. Differential settling of the support posts and pads is caused by setting of the gravel base on unstable ground or by passive solar melting of the frozen subsurface around the perimeter of the unit. Sometimes, the bases are buried in the ground which causes a disturbance to the underlying natural vegetative mat resulting in an unstable and expanding sinkhole as permafrost thaws to new depths. In addition, frost heaving causes similar disturbances to the gravel base and affects the support posts and pads in much the same manner as settling. Collectively, these effects cause some support posts and pads to become disproportionately overloaded or to become suspended. Because the foundation structure of the conventional housing unit is designed for proportionate loads to each of the support posts and pads, the foundation structure undergoes flexing over the more stable posts and pads, as for example, when a corner sinks. The housing unit is then destroyed as a result of such settling. When differential settling occurs in the immediate area of the base, the pad becomes uneven or nonbearing.
The present invention overcomes the major disadvantages of the prior art. The housing unit according to the present invention uses a rigid foundation structure in combination with an integral frame that allows the housing unit to be picked up at the ends and be stacked on top of one another because all the foundation load bearing points will be supported by the frame of the underlying housing unit. In addition, the housing unit of the present invention incorporates an alternative design which uses materials of construction that are capable of spanning the entire length of the housing unit allowing the foundation structure to be supported by a post and pad combination at each corner, thus, eliminating the middle longitudinal beam and associated cross beams and related support posts. Settling in one corner is countered by the rigid foundation and frame which transfer the load to the non-affected support posts and pads without any appreciable sag or flex of the foundation. The affected pad could then be easily raised to relieve the overloading or lowered to increase its load. In addition, the pad of the present invention is braced to the post in such a manner that the pad remains horizontal regardless if there is localized shifting of the immediate base. This is beneficial when only a portion of the base shifts, such that if at least one side of the pad remains in contact with the base, the pad will not canter, but will remain level and able to support its proportionate share of the load. Conventional foundation pads are supported on a leveling course of gravel or in a few cases placed directly on the ground. Gravel is very expensive in many villages as it must be barged in and then often transported over-land without the benefit of roads. Besides the high cost of gravel, another negative is that the gravel becomes a xe2x80x9cheat sinkxe2x80x9d for solar energy. The warm gravel then melts the frozen ground or permafrost below and then causes settling. Most of the time, the gravel pads are actually insulated from the subsurface with expensive rigid insulation. The housing unit of the present invention may rest on the ground, gravel pads or tundra, or alternately and suitably may use sawdust and/or wood chips as a leveling course. The sawdust/chips are inexpensive, lightweight and inexpensive to transport and handle, and provide excellent insulation to help prevent sub-surface thawing. Wood chips/sawdust are also environmentally friendly.
The present invention is a prefabricated housing unit designed to be placed on top of ground bases. The housing unit has a housing shell having longitudinal and transverse lower edges and a foundation structure incorporated into and underlying the housing shell. The foundation structure of the present invention has longitudinal beams that span the entire length of the housing shell edges, and transverse beams that join with the longitudinal beams at the corners. The corner junction is a load bearing point, while the remainder of the longitudinal beams remain substantially unsupported above the ground between the load bearing points.
The preferred embodiment uses a rigid material of construction for the foundation structure and an integral frame that transfers the bending moments from one load bearing point to an adjacent point in the event of a base subsiding into the ground. The integral frame has corner columns that are braced to adjacent columns or to the foundation structure by diagonal braces. The top ends of the columns are interconnected with longitudinal and transverse ties to add to the structure""s rigidity. The corner columns penetrate through the foundation structure. The corner column is preferably hollow to allow a support post to vertically slide within the corner column, allowing adjustment of the height of the support post. A clamp is slidably adjustable on the support post. The clamp bears the load of the lower terminus of the corner column. The lower end of the support post further has a support pad connected by several diagonal braces. The support pad firmly rests on a base. The base is preferably made from fragmented wood materials. The base may have a protective cap of gravel or silt.
The present invention is further directed to a method of designing a prefabricated housing unit such that the combination of foundation structure and integral frame prevent any appreciable sag or bending of the foundation structure. The entire housing unit is supported by load bearing points at or near the corners. Such a design also has the feature of transferring the bending moments from one loading point to adjacent loading points upon subsidence of the ground on which a base rests without appreciable sag or flex of the foundation. The foundation structure and integral frame design also allow the housing units to be hoisted from the ends of the structures and placed on top of each other because all the load bearing points are supported by the underlying housing unit frame. The pad to post connection is designed to allow each pad to bear on any one side upon subsidence of the immediate ground or base on which the pad rests. This suitably includes diagonal bracing of the pad to post, cast into the concrete when concrete pads are used and bolted bracing when we use timber pads. The preferred base material of the present invention also counters the subsidence of the ground due to passive solar radiation.